1. Field of Invention
The present invention relates to polyolefin compositions and particularly to an improvement in polyolefin compositions used under water. More specifically, it relates to polyolefin compositions in which electrical deterioration under water is reduced and to electric cables, connectors and terminals and sheets made from such compositions.
2. Discussion of the Prior Art
Electrical hardware such as electric cables, etc. are often used immersed in water. In such cases, the electrical insulators in the hardware are deteriorated in water. It has been generally known that this deterioration is markedly accelerated when an electrical field is applied to the electrical insulators. It has been found that this deterioration is due to the generation of the so-called water tree. Accordingly, in order to stabilize the operation of this hardware, it is necessary to suppress the generation of water trees in the insulator of electrical machinery such as cables, etc.
The water tree phenomenon is essentially based on a behavior of energetic stabilization by increasing the dielectric constant of a charging space. The water trees generated from a water electrode or a water-containing semiconductive electrode are caused as water, having a high dielectric constant, permeates into the polymeric insulator by the Maxwell force. Further, water trees formed around a void or an impurity in the insulator (so-called "bow tie trees"), water vapor in the polymer condenses and pushes away the polymer chains under electrical charging to thereby mechanically warp the polymer surrounding it. Consequently, the polymer creeps and microcrystals come loose, by which water is scattered from an orifice formed on the void wall.